Hybrid Encapsulated Ionic Liquids for Post-Combustion Carbon Dioxide (CO2) Capture
- Univ. of Texas, Austin, TX (United States)
- Univ. of Notre Dame, IN (United States)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
It is increasingly clear that carbon dioxide (CO2) capture and sequestration (CCS) must play a critical role in curbing worldwide CO2 emissions to the atmosphere. Previously, we have developed ionic liquids (ILs) and phase change ionic liquids (PCILs) for post-combustion CO2 capture. In this project, we synthesized and tested 19 ILs and PCILs and chose one of each for further development. The IL selected for further development was triethyl(octyl)phosphonium 2-cyanopyrrolide ([P2228][2CNPyr]), which has the same anion but a different cation, than used in our previous work. The new cation imparts a lower viscosity than the prior cation. The PCIL selected for further development was tetraethylphosphonium benzimidazolide ([P2222][BnIm]), which was developed in an Advanced Research Projects Agency-Energy (ARPA-E) project. Although we made numerous other candidates, none were better than this original PCIL. Here we showed that the CO2 absorption by the IL and the PCIL was completely reversible, even when water was present. We determined and quantified the additional chemistry, involving the formation of bicarbonate, when water is present. The IL and PCIL were encapsulated in silicone shells using a microfluidic device. Compatibility between the IL/PCIL and the polymer, viscosity, and surface tension issues, getting sufficiently high IL/PCIL loading and leakage (likely from insufficient cross-linking), were serious challenges. Small quantities (~ 1 g) of microcapsules with good integrity of both the IL and the PCIL were produced. The CO2 uptake by these capsules was the same as for the free IL and PCIL and the capacity of the capsules decreased only slightly even after five absorption and desorption cycles. As expected, the IL and PCIL (and subsequently the encapsulated IL and PCIL) reacted readily with SO2 and NO, so, like aqueous amine absorbents, the CO2 capture unit would have to be located downstream of the flue gas desulfurization and other gas treatment units. Large samples (~70 g and 100 g) of encapsulated PCIL were produced in a parallel microfluidic device and in an in-air device. These capsules were tested in a Laboratory Scale Unit (LSU) to demonstrate uptake capacity in a fluidized bed. We also used the LSU to determine recyclability and mass transfer coefficients. Unfortunately, equivalent experiments with the IL were not possible due to difficulties with producing large samples of the encapsulated IL. This IL encapsulation “scale-up” problem was not solved during the course of this project. Nonetheless, using the PCIL microcapsules we demonstrated that, as expected, the mass transfer is internally controlled. In concert with a new rate-based model of the fluidized bed, we determined that the productivity is increased by a factor of 4.75 in the microcapsule fluidized bed absorber compared to a conventional liquid-gas packed bed absorber. The initial technoeconomic model shows that the capital cost for the microcapsule IL continuous fluidized bed process is similar to that of an aqueous amine process (specifically, the Econamine FG Plus technology). However, the stripping heat requirements are about 35% less for the model IL microcapsule case compared to the monoethanolamine (MEA) case. Thus, encapsulated ILs/PCILs in a continuous fluidized bed absorber for post-combustion CO2 capture are a significant improvement over the free IL/PCIL case and represent a major reduction in the parasitic energy requirements compared to aqueous amine process.
- Research Organization:
- Univ. of Notre Dame, IN (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- FE0026465
- OSTI ID:
- 1530159
- Report Number(s):
- Final; DUNS Number: 824910376
- Resource Relation:
- Related Information: None
- Country of Publication:
- United States
- Language:
- English
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